DP83261 datasheet(95/132 Pages) NSC

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70 Signal Descriptions (Continued)

743 Operation

The MAC Request Interface has three logical states as determined by TXRDY and TXPASS The interface state machine is

shown in

Figure 7-11 followed by a description of the conditions states and transitions

State

Description

TXRDY

TXPASS

MR0 Not Ready

Ring Engine is not ready to service a request

MR1 Ready

Ring Engine is ready to transmit a frame

MR2 Sending

Ring Engine is sending a frame

TLF10387 – 18

FIGURE 7-11 MAC Request Interface State Machine

Conditions

Send Frame

A frame can be sent from the interface when at least 8 bytes of preamble have been transmit-

ted TXRDY RQRDY and RQSEND are asserted and RQFINAL has not yet been asserted for

this request

Service Opportunity

A Service Opportunity occurs when it is possible to service the current request as defined by

the current service parameters (RQRCLS RQCLM and RQBCN) The rules for servicing re-

quests are described in Section 52

Continue Service Opportunity

A Service Opportunity is continued after the current frame if valid service parameters continue

to be presented during the frame and the timer(s) used for the (next) requested service class

have not reached their threshold

End of Service Opportunity

The end of a Service Opportunity occurs when it is no longer necessary or possible to continue

the Service Opportunity The service parameters are continuously compared with the current

state of the Transmitter If an unserviceable request is presented or any timer threshold is

reached the Service Opportunity will not continue after the current frame (if any)

Table 7-4 shows the timer thresholds used to determine if a Service Opportunity is possible for each service class

TABLE 7-4 Thresholds Used to Determine Service Opportunities

Request Service Class

Threshold

All Requests

TRT Expiration

All Requests with THT Enabled

THT Expiration

Priority Asynchronous Requests

Asynchronous Priority Threshold

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